Joydip Ghosh

Zwitterion-assisted growth yields low-defect FAPbBr ₃ single crystals, while optimised temperature ramping reduces strain. The devices show high charge transport, ultra-low dark current, and excellent room-temperature α-particle and X-ray detection.

Lead-free perovskite-inspired materials have emerged as promising candidates for direct X-ray detection. However, in the early exploration of emerging materials, the focus was on large single crystals. Herein, we report a facile, scalable, single-step synthesis of high-quality Cs₃Bi₂I₉ nanocrystals (NCs) directly from their precursor powders through an ultrasonication approach. The large-scale synthesis of the NCs allowed for the production of 0.78 cm² pellets used in the fabrication of X-ray detection devices, which exhibit a high bulk resistivity of 1 × 10¹¹ Ω cm and a low dark current density of 3.3 nA cm^–2 under an applied bias of 50 V (357 V cm^–1 electric field). These devices achieve a limit detection of 108 nGy_air s^–1, an order of magnitude improvement over the a-Se used in commercial medical imaging, along with stable current under continuous X-ray exposure with a peak energy of 35 keV_p. Finally, we demonstrate the scale-up of these detectors by producing thick films 9 cm² in area, achieving a performance comparable to that of the detectors based on pellets.

In this study, the investigation of a Cs₂AgBiBr₆ single crystal (SC) / CsPbBr₃ nanocrystals (NCs) film double perovskite/perovskite type‐II novel heterojunction tailored for superior X‐ray detection applications is presented. One of the main benefits of utilizing such a heterojunction is its built‐in electric potential, which improves charge transport and reduces the dark current in the devices. By casting CsPbBr₃ NCs onto polished Cs₂AgBiBr₆ SC, the Cs₂AgBiBr₆/CsPbBr₃ double perovskite/ perovskite heterojunction is fabricated. The heterojunction X‐ray detector exhibits reduced dark current and increased photocurrent compared to the pristine SC device. This enhancement of photocurrent can be attributed to efficient carrier generation and separation facilitated by appropriate band bending at the type‐II heterojunction interface. The heterojunction device shows an X‐ray sensitivity of 6 µCGy⁻¹ cm⁻² at 0 V of applied bias, owing to the built‐in potential across the heterojunction. Remarkably, at a −50 V bias, the sensitivity of the heterojunction device reached 857.8 µCGy⁻¹ cm⁻², with a limit of detection of 312 nGy s⁻¹. Density functional theory (DFT) calculations provided further insights, revealing electron transfer from CsPbBr₃ to Cs₂AgBiBr₆, thereby enhancing the X‐ray sensitivity of the heterojunction device. These findings underscore the potential of Cs₂AgBiBr₆/CsPbBr₃ heterojunctions for X‐ray detection and optoelectronic applications.

This article details work performed on the synthesis and characterization of an inorganic mixed‐cation double halide perovskite, Cs₂Ag_.6Na_.4In_.85Bi_.15Cl₆ (CANIBIC). Single crystals have been created via a hydrothermal reaction, milled into a powder, and pressed into pellets, while nanocrystals have been directly synthesized via mechanosynthesis. A computational model is constructed to predict the X‐ray diffraction pattern of CANIBIC; this model aligns very well with the X‐ray diffraction pattern measured for CANIBIC crystal powder. This model can therefore be developed in the future as a tool to predict lattice parameters and crystal structures of other novel double‐halide perovskites. Photoluminescence spectra obtained from each format show broad emission centered at 630 nm, as is typical for self‐trapped exciton emission; self‐trapped exciton emission is also confirmed by investigating photoluminescence intensity as a function of laser power. Nanocomposites are produced via the loading of nanocrystals of CANIBIC into PMMA. Although nanocomposite disks consisting of a small proportion of CANIBIC nanocrystals in PMMA have a smaller mass attenuation coefficient than a pressed pellet of CANIBIC, these disks have comparatively bright radioluminescence due to their optical transparency. These nanocomposite disks are therefore a particularly useful format for the practical use of the CANIBIC scintillator.

We report a facile, solvent-free surfactant-dependent mechanochemical synthesis of highly luminescent CsPbBr₃ nanocrystals (NCs) and study their scintillation properties. A small amount of surfactant oleylamine (OAM) plays an important role in the two-step ball milling method to control the size and emission properties of the NCs. The solid-state synthesized perovskite NCs exhibit a high photoluminescence quantum yield (PLQY) of up to 88% with excellent stability. CsPbBr₃ NCs capped with different amounts of surfactant were dispersed in toluene and mixed with polymethyl methacrylate (PMMA) polymer and cast into scintillator discs. With increasing concentration of OAM during synthesis, the PL yield of CsPbBr₃/PMMA nanocomposite was increased, which is attributed to reduced NC aggregation and PL quenching. We also varied the perovskite loading concentration in the nanocomposite and studied the resulting emission properties. The most intense PL emission was observed from the 2% perovskite-loaded disc, while the 10% loaded disc exhibited the highest radioluminescence (RL) emission from 50 kV X-rays. The strong RL yield may be attributed to the deep penetration of X-rays into the composite, combined with the large interaction cross-section of the X-rays with the high-Z atoms within the NCs. The nanocomposite disc shows an intense RL emission peak centered at 536 nm and a fast RL decay time of 29.4 ns. Further, we have demonstrated the X-ray imaging performance of a 10% CsPbBr₃ NC-loaded nanocomposite disc.